Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02326369 2000-11-20
R. R. Goodrich 15
MODULAR JACK HAVING A
PLUG-POSITIONING MEMBER
Technical Field
This invention relates to connectors used in electrical communications and,
more particularly, to the electrical and physical design of a modular jack.
Background of the Invention
The term crosstalk was originally coined to indicate the presence in a
telephone receiver of unwanted speech sounds from another telephone
1o conversation. Of particular interest is crosstalk that is caused by signal
coupling
between adjacent circuits. The most common coupling is due to near-field
effects
and can usually be characterized by mutual inductance and direct capacitance.
This
is best illustrated by considering two parallel balanced transmission paths.
One
circuit (the disturbing circuit) is a source of signal energy that is
undesirably
15 coupled into an adjacent circuit via stray capacitance and mutual
inductance. Near-
end crosstalk (NEXT) is crosstalk energy that travels in the opposite
direction to
that of the signal in the disturbing circuit, whereas far-eud crosstalk is
crosstalk
energy that travels in the same direction as the signal in the disturbing
circuit.
Circuit analysis indicates that NEXT is frequency dependent and, for
2o communication connectors, its magnitude typically increases with frequency
at a
6.0 dB per octave rate. NEXT is introduced within an electrical cable as a
result of
signal energy being coupled between nearby wires; and within an electrical
connector, particularly modular plugs and jacks, as a result of signal energy
being
coupled between nearby conductors. NEXT is undesirable and is frequently
25 referred to as offending crosstalk.
U. S. Patent 5,096,442 discloses a modular jack whose NEXT is about 25
dB below the level of the incoming signal at 100 MHz. Such NEXT is
attributable
to crosstalk that is introduced by the combination of a standard modular plug
with
a standard modular jack such as are generally used for voice-grade
3o communications. However, this level of crosstalk is generally too high for
modern
high-speed data applications.
U. S. Patent 5,186,647 discloses a substantial improvement to the design of
a standard modular jack by crossing the path of one of the conductors within
the
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R. R. Goodrich 15 - 2
jack, over the path of another of the conductors within the jack to produce
crosstalk
of an opposite polarity. Such compensating crosstalk attempts to cancel NEXT
rather than merely minimizing it by, for example, increasing the separation
between conductors. This simple technique improves NEXT at 100 MHz by a
startling 17 dB, thereby enabling popular modular jacks to meet Category 5
requirements specified in ANS1/EIAlTIA - 568A. An example of such a modular
jack is the M100 Communication Outlet, which is manufactured by Lucent
Technologies Inc.
Techniques have been developed that further improve the crosstalk
1o performance of an electrical connector so that NEXT is now more than 60 dB
below the level of the incoming signal at 100 MHz. U. S. Patent 5,997,358
shows
such,techniques. However, this level of crosstalk performance represents the
very
best that can be attained since crosstalk will vary according to how the plug
is
seated within the jack. At least one manufacturer has disposed the jack
springs
t5 within the modular jack at a relatively large contact angle (about
36°) with respect
to the longitudinal axis of the modular jack in order to push the modular plug
into a
fixed location within the jack. However, since there are many jack springs
that
need to make electrical contact with the blades of an inserted modular plug,
large
contact angles make this task difficult. Whereas large contact angles create
2o increased pressure against the plug blades, increased pressure by some of
the jack
springs can preclude other spring contacts from making contact with the plug
blades unless the plug blades and the jack springs are all precisely aligned.
Indeed,
current FCC standards recommend a relatively small contact angle (i.e.,
between
13 and 24 degrees) to assure that all plug blades make contact with the jack
25 springs.
Accordingly, what the prior art appears to lack and what is now desired is a
technique for assuring the consistent positioning of a modular plug within a
modular jack, where the modular jack includes jack springs that are disposed
at
relatively small angles with respect to the longitudinal axis of the jack.
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R. R. Goodrich 15 - 3 -
Summary of the Invention
A modular jack includes a jack housing with an opening in its front end that
is adapted to receive a modular plug. Within the opening there are a number of
jack springs for making electrical contact with metallic blades that are
installed in
the plug. Variations in the actual position where the plug blades make contact
with
the jack springs are reduced by the inclusion of a positioning member within
the
jack. The positioning member engages the modular plug to create an axial force
that pushes the plug toward a fixed retaining surface within the jack thereby
reducing positional variation between the plug and the jack contact interface.
to Reduced positional variation is particularly important in situations where
the modular plug includes crosstalk compensation since positional variation
affects
the amount of crosstalk compensation needed.
In one illustrative embodiment, the positioning member comprises a cam
that is molded into the housing and is positioned to engage a flexible latch
on the
t5 modular plug. The interaction between the cam and the flexible latch
creates an
axial force that pushes the plug toward a fixed retaining surface within the
housing.
As a result, the plug is pushed into a known position within the jack.
In another illustrative embodiment, the positioning member comprises a
spring, other than the jack springs, that engages a rigid surface on the
modular plug
20 to create an axial force that pushes the plug toward the fixed retaining
surface.
Advantageously, in both embodiments, the.improved modular jack is compatible
with existing modular plugs.
Brief Descriution of the Drawing
The invention and its mode of operation will be more clearly understood
25 from the following detailed description when read with the appended drawing
in
which:
FIG. 1 shows an assembly of interconnecting hardware, which is used in an
electrical communication system;
FIG. 2 is a top side perspective view of a modular plug;
3o FIG. 3 is a bottom side perspective view of the modular plug being inserted
into a first embodiment of a modular jack according to the present invention;
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R. R. Goodrich 15 - 4 _
FIG. 4 shows a cross-section view of the first embodiment of the invention
with the modular plug installed within the modular jack;
FIG. 5 is a bottom side perspective view of the modular plug being inserted
into a second.embodiment of a modular jack according to the present invention;
and
FIG. 6 shows a cross-section view of the second embodiment of the
invention with the modular plug installed within the modular jack.
Detailed Description
FIG. 1 discloses an assembly of interconnecting hardware, which is used in
to an electrical communication system. This hardware is illustratively used to
interconnect a high-speed computer station 300 to an electrical cable 20 via
standard telecommunications connecting apparatus such as a cord 30, a modular
plug 100, and a modular jack 200. Specifications for such plugs and jacks can
be
found in subpart F of the FCC Part 68.500 Registration Rules. Modular jack 200
t5 comprises a spring block assembly 210 and a jack housing 220 that interlock
together to provide a convenient receptacle for receiving and holding the
modular
plug 100. Spring block assembly 210 includes a number of electrically
conductive
paths. The conductive paths terminate, at one end, in flexible wire springs
(hereinafter "jack springs") that ace made, for example, from a resilient
material
2o such as beryllium-copper and are arrayed within the modular jack to make
electrical contact with a corresponding array of metallic blades 120 within
the
modular plug (see Fig. 2). The conductive paths terminate in insulation-
displacement connectors, at the other end, that make electrical contact with
the
wires in cable 20. Examples of known spring block assemblies are shown in U.S.
25 Patents 5,041,018 and 5,096,442 and are designed to be installed into the
back end
of a jack housing 220.
An opening 225 in the front end of jack housing 220 is shaped to receive
the modular plug 100, which is inserted and held therein. However, even though
the modular plug is locked within the modular jack via cantilever latch 130
(see
3o FIG. 2), its blades 120 may contact the jack springs anywhere over range of
positions according to how deeply the plug is inserted. This is known as
positional
variation, and the present invention seeks to reduce or eliminate it. And
while
positional variation is not a problem for voice frequency communications, it
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R. R. Goodrich 15 - 5
adversely affects electrical performance at higher frequencies. A wall plate
400 is
frequently used to support the modular jack 200, which is installed into an
opening
410 in the wall plate that is designed to hold the jack.
FIG. 2 is a perspective view of a standard modular plug 100 illustrating its
general construction. Modular plug 100 comprises a dielectric plug housing 110
having a number of metallic terminals 120, which are inserted into a plurality
of
terminal-receiving slots. In FIG. 2 there are eight such slots (101-1 through
101-8)
that extend downward from the top side of the housing into conductor-receiving
ducts that hold the wires from cord 30. Plug housing 110 includes a rigid
front
1o surface 135 and a conductor strain relief member 140, which is deflected
downward during assembly to anchor the conductors in engagement with the
bottom of a chamber within the plug in order to provide strain relief for the
conductors. Plug housing 100 further includes a jacket strain relief member
150,
which is also deflected downward during assembly in order to provide strain
relief
t5 for the jacket of cord 30. A cantilever latch 130 is provided for locking
the plug
100 with the modular jack 200. At this point, it is noted that the present
invention
deals with modifications to the modular jack that reduce axial movement of a
modular plug 100 within a modular jack 200. In particular, modular jack 200 is
adapted to reduce axial movement of standard modular plugs.
20 Near-End Crosstalk
As discussed in the Background of the Invention, crosstalk between pairs of
conductors within a modular jack can be significantly reduced by adding
compensating crosstalk within the jack. Compensating crosstalk has a polarity,
which is opposite the polarity of the offending crosstalk, and is deliberately
25 introduced in an attempt to cancel the offending crosstalk. Moreover, it is
important that: ( 1 ) the compensating crosstalk be introduced as close as
possible to
the offending crosstalk; and (2) the compensating crosstalk be introduced at a
consistent location within the modular jack. These considerations recognize
that at
high frequencies (i.e., frequencies equal to or greater than 100 MHz) the hase
of
3o the compensating crosstalk changes significantly over short distances, and
it is
essentially impossible to introduce compensating crosstalk that is exactly 180
degrees out of phase with the offending crosstalk because of propagation
delay.
This has caused designers to introduce the compensating crosstalk within the
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R. R. Goodrich 15 - 6 -
modular jack as close as possible to the location where the jack springs make
contact with the blades in the modular plug; and to keep that location
constant.
The present invention achieves these goals as illustrated in the embodiment of
FIG.
3.
FIG. 3 is a perspective view of a modular plug 100, having a cord 30
attached thereto, that is about to be inserted into an opening 225 in the
front end
221 of modular jack 200. Insertion is achieved by advancing the plug 100 along
the longitudinal axis 201-201 of the jack into the opening 225. It is noted
that this
design provides a limited amount of plug travel "dl," which is approximately
0.033
to inches (0.84 millimeters) until the plug is pushed against a back retaining
surface
214. Once the plug is fully inserted into the jack 200, plug blades 120 make
electrical contact with jack springs 215 in the location designated 211. It is
desirable for location 211 to be close to location 212 so that offending
crosstalk,
which is introduced in the region between 211 and 212, is minimized. It is
15 particularly important to know the exact distance "d" between these
locations
because variations in this distance change the magnitude and phase of the
offending
crosstalk that needs to be canceled. Thus, by reducing the variation of
distance "d,"
the compensating crosstalk provided by the modular jack can be more accurately
designed to cancel the o, fj''ending crosstalk. It is noted that compensating
crosstalk
20 may be introduced by techniques other than crossing jack springs 215, and
that the
present invention may be used in ~ modular jack that would benefit from
reduced
variation of the location 211 where electrical contact is made between the
plug
blades 120 and the jack springs 215.
In accordance with the present invention, the variation of distance "d" is
25 reduced by reducing the variation of location 211. This is accomplished by
including a positioning member within the modular jack 200 that causes an
inserted modular plug 100 to be consistently seated in a known position. Once
the
plug is inserted into the jack, it is pushed forward or backward until it
encounters a
retaining surface that stops further movement in that direction. In accordance
with
3o a first embodiment of the present invention shown in FIGS 3 and 4,
advantageous
use is made of the flexible cantilever latch 130, which is present on all
standard
modular plugs, that flexes in order to allow the plug to enter an opening 225
in the
front end 221 of the modular jack 200. In this embodiment the positioning
member
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_7_
comprises a cam 228 that interacts with an angled (about 60° with
respect to the
longitudinal axis 201) surface 131 on the cantilever latch to create a force
"F1"
that tends to push the modular plug out of the jack housing 220. This force
"F1"
is created by the restorative force of the cantilever latch 130 as it attempts
to
return to its original, non-flexed state. However, the jack housing includes a
forward retaining surface 229, which engages a stop surface 132 on the
cantilever
latch and thereby prevents the plug from becoming decoupled from the jack
housing. Advantageously, the plug 100 has reduced positional variation.
FCC standards for modular plugs and jacks allow for approximately 0.033 inches
(0.84 millimeters) of axial positional freedom. When the jack springs 215 are
disposed at an acute angle cp of 17°, for example, with respect to the
longitudinal
axis 201-201, then the actual variation in transmission path length "d" is
approximately 0.035 inches (0.89 millimeters). Since additional offending
crosstalk is introduced in the region between locations 211 and 212, whose
t5 distance "d" is approximately 0.148 inches (3.76 millimeters), then
eliminating
the FCC-allowed positional variation by a maximum of 0.035 inches
(0.89 millimeters) (or 23%) likewise reducing the variation of the offending
crosstalk in this region. And while the offending crosstalk is increased
slightly
owing to the direction of "F1 ", it can be canceled more precisely because it
is
precisely known.
Tt is noted that FIGS. 3 and 4 do not show with any particularity how the
jack springs 215 are mounted within the spring block assembly 210, such detail
is
relatively unimportant to the present invention and, if shown, would tend to
confuse the reader. Nevertheless, now that the basic operation of one
embodiment
of the invention has been shown and described, a second embodiment will now be
disclosed that reveals greater detail regarding the actual construction of the
modular jack 200.
FIGS. 5 and 6 disclose a second embodiment of the present invention,
which reveals detail regarding the construction of modular jack 200. In
particular,
modular jack 200 comprises a spring block assembly 210 that is installed into
the
back end of jack housing 220. The jack springs 215 are mounted on a structure
216 that includes circuitry for introducing capacitive and/or inductive
coupling
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_g_
between selected pairs of conductors in order to provide compensating
crosstalk
as discussed above. United States Patent No. 6,116,964, issued
September 12, 2000, provides detailed information regarding the design of
spring
block assembly 210. In the second embodiment, the positioning member
comprises a resilient leaf spring 213, illustratively made from a metallic
material
such as beryllium-copper, that is mounted in a front-end portion of the spring
block assembly 210. Once the modular plug 100, the jack frame 220 and the
spring block assembly 210 are joined together as shown in FIG. 6, the flexible
leaf
spring 213 is positioned to interact with the rigid front surface 135 of the
modular
to plug 100 in order to create a force "F2" that tends to push the modular
plug out of
the jack housing 220. This force "F2" is created by the restorative force of
the
spring 213 as it attempts to return to its original, non-flexed state.
However, the
jack housing includes a forward retaining surface 229, which engages a stop
surface 132 on the cantilever latch and thereby prevents the plug from
becoming
decoupled from the jack housing. Advantageously, the distance "d" between
location 211 (where the jack springs 215 make contact with the plug blades
120)
and location 212 (where crosstalk compensation is introduced) is relatively
constant. Accordingly, this second embodiment also provides the desired
consistent positioning of a modular plug within a modular jack.
2o Although various particular embodiments of the present invention have
been shown and described, modifications are possible within the scope of the
present invention. These modifications include, but are not limited to: the
use of
positioning members that force the modular plug more deeply into the modular
jack; the use of multiple positioning members within the modular jack; the use
of
an elastomeric material such as rubber as the positioning member; and the use
of
materials other than those shown in this specification in the construction of
the
modular jack.
